SummitGunBroker does have great prices. Both my roommate and I bought G17s from him. He is careless though. Maybe he has really high volumes of sales, and we just happened to get two of his few mistakes. I had to send my first G17 back because it arrived with a buldged barrel. The mags also looked like someone used them as an eraser on concrete. One is a POS and doesn't always work reliably, but the other two are fine. The replacement pistol I received functions 100% and has the older, grey finish which I prefer.
My roommates G17 was almost brand new. He ordered it with nightsights and it came with Mepros. He got BRAND NEW mags, but one was a .40cal. He replaced it with a 9mm mag for free.
Still the prices are hard to beat, and turnaround is not bad. I'll order more stuff from him, even with the flaws we experienced.
I've heard a lot of good about CDNN and they're the best place for mags that I've seen.